Will salt water weaken rice leaf miners?

Will the South American rice leaf miner be affected by salt water pushed ashore by Hurricane Rita? LSU AgCenter entomologist Boris Castro said it’s possible the rice pest’s population could have been weakened by the high salinity, but there’s no way of knowing now because the insect has only been known to be in the country the past couple of growing seasons.

“We don’t know where it overwinters,” Castro said, explaining the pest first appeared in 2004 but was not identified until 2005.

The LSU AgCenter researcher said he was surprised that the amount of damage in Louisiana rice fields increased significantly last year. “It was even worse than the year before,” he said of 2004, when the pest first appeared but had yet to be identified as the cause of damage.

At the Louisiana Agricultural Consultants Association convention in Alexandria, La., Castro said that the South American rice leaf miner inflicted most of its devastation on coastal rice fields.

The insect also was found last year in north Louisiana, but it had little effect on rice fields there, Castro said, possibly because the insect seems to have a preference for more tropical environments.

In 2004, the rice leaf miner was found in Acadia, St. Landry, Vermilion, Jefferson Davis and Concordia parishes. In 2005, Castro also found it in Cameron, Allen, St. Martin and Tensas parishes.

“As far as control, we still don’t have a chemical,” he said.

Methyl parathion had no effect on a Cameron Parish rice field of 230 acres hit by the tiny insect last season, Castro said. “That was the worst infestation,” he said. “It was a complete loss.”

A field of 150 acres in Vermilion Parish also was ruined by the pest in 2005.

“The infestation that started on one side of the field reached the other end in three days,” Castro said, adding, however, that an adjacent field wasn’t attacked.

The insect prefers late-planted rice, according to Castro, who pointed out the 230-acre field in Cameron Parish had been planted in early June. Castro said he didn’t find the insect in any rice fields planted within the usual window of late March through April.

The adult fly of this insect species is about the size of a pinhead. The larvae, or maggot, infests the leaves of the young plants, feeding on the plant’s growth tissue.

“It kills the growing part, and then the tiller is dead,” Castro said.

In an interview, Castro said there’s usually not much that can be done by the time the pest strikes. “It’s frustrating, because when they call us, it’s often too late,” he said.

The LSU AgCenter plans to conduct studies on biological aspects and behavior of this tiny pest, according to Castro, who said researchers also will investigate the effect of seeding rates, water management, varietal preference and the use of systemic insecticides.

“However, as of now, the only recommendation available is to avoid late planting of rice,” he said. “Rice planted beyond mid-May, especially in southwestern coastal parishes of Louisiana, has increased risks of a direct hit by the South American rice leaf miner.”